(1) Field of the Invention
This invention relates to RF transformers. More particularly, the present invention is directed to RF transformers particularly well-suited to be employed for exciting gas lasers with a transverse RF discharge and to a diagnostic technique therefor. Accordingly, the general objects of the present invention are to provide novel and improved apparatus and methods of such character.
(2) Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well-suited for use in association with RF excited gas lasers. U.S. Pat. Nos. 4,169,251, 4,352,188, 4,363,126, 4,429,398 and 4,443,877 generally disclose RF excited gas lasers which employ two opposing conducting surfaces between which a transverse gas discharge is created. U.S. Pat. No. 4,169,251 discloses a wave guide laser which is excited by means of a transverse discharge at sufficiently high RF frequencies to insure negligible interaction of discharge electrons with the discharge establishing electrodes. U.S. Pat. No. 4,352,188 discloses an RF pumped wave guide laser wherein a transverse RF excitation voltage at a frequency of at least thirty (30) MHz is applied between elongated electrodes on opposite sides of a laser discharge chamber. A plurality of shunt inductances are coupled between the opposing electrodes externally of the chamber a periodically spaced positions along the length of the chamber to provide a negative admittance which compensates for the variation of the phase angle of the transmission line reflection coefficient along the length of the laser discharge chamber. The variation in the magnitude of the voltage standing wave ratio (VSWR) along the laser chamber produced by the excitation voltage is thereby reduced.
U.S. Pat. No. 4,363,126 discloses an RF excited gas laser which employs a tuned circuit having a resonant frequency wherein the real part of the complex impedance of the discharge chamber is matched to the output impedance of a driving oscillator by placing an inductive element in parallel with the laser discharge chamber resistance and capacitance. The value of the inductance is selected so that the resonant frequency of the discharge chamber tuned circuit created by the addition of the inductive element has a predetermined relationship to the RF driving frequency of the laser. An input circuit compensates for the reactive part of the discharge chamber impedance.
A principal technical problem associated with RF excited gas lasers is the transmission line effects which result from increasing the electrical length of the laser or the excitation frequency of the laser, the electrical length of a laser being proportional to the excitation frequency and the physical length of the laser. Increasing the electrical length of the laser tends to adversely affect the discharge uniformity and consequently reduces the operating efficiency and the obtainable output power of the laser resulting in a laser with low output power per unit length. Another principal deficiency of conventional RF excited gas lasers is the inefficient power transfer between the RF driving source and the gas discharge.